Rulings
Q1: When exactly is the timing when this card's Trash All Turns effect triggers?
It triggers at the timing when this card is in the trash and your Dorugamon would be deleted. Trash means that an effect can trigger and activate when the card is in the trash.
Q2: If I use this card's Trash effect to digivolve when my Dorugamon would be deleted by its DP becoming 0, can I prevent that deletion?
Yes, you can. However, the DP-reducing effect will be carried over after the Trash effect activates and digivolution occurs, therefore deletion will occur again if the DP is still 0 after the effect activates and digivolution occurs.
Q3: I used this card's Trash effect to digivolve when my Dorugamon would be deleted due to its DP being reduced by 10000. Its DP became 0 due to the DP-reducing effect, but can I activate this card's When Digivolving effect after it digivolves at such times?
No, you can't activate it. The Digimon is deleted before the When Digivolving effect activates.
Q4: Does "delete 1 of your opponent's Digimon with a play cost of 4 or less instead" in this card's When Digivolving effect activate instead of "Trash 1 card in your hand. Then, Draw 1"?
No, it activates instead of "Then, Draw 1."
Data Sources
Lv.4 DexDorugamon BT17-065 C Champion | Virus | Undead/X Antibody/SoC [Digivolve] [Dorugamon]: Cost 0 [Trash] [All Turns] When one of your [Dorugamon] would be deleted, by digivolving it into this card without paying the cost, prevent that deletion. [When Digivolving] Trash 1 card in your hand. Then, <Draw 1>. If [Dorugamon] is in this Digimon's digivolution cards or this digivolved from the trash, delete 1 of your opponent's Digimon with a play cost of 4 or less instead. --- Inherited: <Reboot> (This Digimon also unsuspends during your opponent's unsuspend phase.)
Lv.4 DexDorugamon BT17-065 C Champion | Virus | Undead/X Antibody/SoC [Digivolve] [Dorugamon]: Cost 0 [Trash] [All Turns] When one of your [Dorugamon] would be deleted, by digivolving it into this card without paying the cost, prevent that deletion. [When Digivolving] Trash 1 card in your hand. Then, <Draw 1>. If [Dorugamon] is in this Digimon's digivolution cards or this digivolved from the trash, delete 1 of your opponent's Digimon with a play cost of 4 or less instead. --- Inherited: <Reboot> (This Digimon also unsuspends during your opponent's unsuspend phase.)
Lv.4 DexDorugamon BT17-065 C Champion | Virus | Undead/X Antibody/SoC [Digivolve] [Dorugamon]: Cost 0 [Trash] [All Turns] When one of your [Dorugamon] would be deleted, by digivolving it into this card without paying the cost, prevent that deletion. [When Digivolving] Trash 1 card in your hand. Then, <Draw 1>. If [Dorugamon] is in this Digimon's digivolution cards or this digivolved from the trash, delete 1 of your opponent's Digimon with a play cost of 4 or less instead. --- Inherited: <Reboot>.
Lv.4 デクスドルガモン BT17-065 C 成熟期 | ウィルス種 | アンデッド型/X抗体/SoC 「ドルガモン」:コスト0 [トラッシュ]【お互いのターン】自分の「ドルガモン」が消滅するとき、そのデジモンをこのカードにコストを支払わずに進化させることで、消滅しない。 【進化時】自分の手札を1枚破棄する。その後、≪1ドロー≫。このデジモンの進化元に「ドルガモン」があるか、トラッシュから進化していたなら、代わりに登場コスト4以下の相手のデジモン1体を消滅させる。 --- Inherited: ≪再起動≫（このデジモンは相手のアクティブフェイズでもアクティブになる）